It is well known in the art to utilize the zinc-rich primer materials for providing corrosion resistant coatings on metal surfaces, such as upon the sheet metal body components of automotive vehicles. Such primer coatings utilize fine zinc particles, and in the presence of a corrosive atmosphere, the steel body components are protected at the expense of the zinc particles, since the electrical potential of the zinc is sufficiently higher than that of a steel to direct the flow of electrons to the steel, maintaining a negative charge on the steel surface and preventing the formation of ferrous ions which represent corrosion or rust. This effect results in the formation of zinc hydroxide on the zinc which in turn reacts with chlorine or carbon dioxide in the surrounding environment to form basic zinc salts. These basic zinc salts plate out on the bare steel surface to form a protective coating which affords good barrier protection to the steel. When this effect is taking place, the metallic zinc is, of course, being consumed by the salt formation; thus the term "sacrifical action".
While such sacrificial-type primer compositions have found wide commercial use, zinc-rich primer materials per se suffer a number of shortcomings over which the priming material or composition of the present invention are intended to overcome. One of the primary shortcomings of zinc-rich primers resides on the cost thereof, resulting from the high cost of the zinc embodied therein. A related problem, of course, resides in the limited availability of the zinc material embodied in such zinc-rich primers. The primer material of the present invention, on the other hand, does not utilize zinc and thus may be commercially manufactured at a cost of approximately one-half (50%) that of zinc-rich primers, and it is therefore one important object of the present invention to provide a corrosion resistant primer material which may be manufactured at a significantly lower cost of comparable zinc-rich primers.
An additional shortcoming of zinc-rich primers resides in its relatively low flash point, i.e., in the order of 80.degree. F. which results in severe limitations as to bulk use. The primer material of the present invention has a flash point in excess of 100.degree. F. and therefore can be used almost without limitation in bulk form.
Another significant drawback of zinc-rich primers resides in the high magnitude of weight per gallon, which is typically in the order of 22 pounds per gallon. The primer material of the present invention, on the other hand, weighs approximately 9 pounds per gallon, thereby permitting the use of significantly larger containers, with a resultant savings in container costs and ancillary shipping expenses.
yet another extremely important drawback of primer materials heretofore known and used results in the fundamental degree of corrosion reistance provided thereby. While zinc-rich primers are capable of surviving only 250-500 hour salt spray tests commonly utilized in the automotive industry, the primer material of the present invention is capable of and has survived identical salt spray tests lasting for up to 1,000 hours. Accordingly, it is another important object of the present invention to provide an improved primer material which exhibits improved corrosion resistant properties as compared to zinc-rich primers heretofore known and used.
Still another fundamental shortcoming of zinc-rich primers resides in the fact that once the entire quantity of zinc has been consumed as a result of the sacrificial process, the corrosion resistant properties afforded by such materials is essentially terminated; however, since the primer material of the present invention does not operate on a sacrificial principle, the corosion resistant properties thereof last essentially indefinitely.
A further shortcoming of zinc-rich primers, insofar as the automotive industry is concerned, results from the phosphating process to which body parts are subjected preparatory to painting in order to remove oil films and the like. Since such phosphating processes occur after the primer material has been applied, zinc-rich primers have been found to be objectionable in that the zinc is attacked by the phosphating chemicals. Such is not the case with the primer material of the present invention since no zinc is utilized therein and thus the primer material is completely unaffected by the phosphating operations.
Still another shortcoming of zinc-rich primers of the type heretofore known and used results in the creation of stress areas on body components which are subjected to certain types of welding operations. Typically, such problems arrise in connection with the welding of hem flanges, for example, on automobile doors. In view of the fact that the corrosion resistant coating material of the present invention is entirely devoid of sacrificial material, such as zinc, no such stress areas occur and thus there is no likelihood of corrosion being created on the metal component at the areas of the welds formed therein. An additional shortcoming of zinc-rich primers resides in the aforementioned low flash point which results in objectionable burn-through areas during welding operations.
The corrosion resistant coating material of the present invention will also be found to be superior to zinc-rich coatings heretofore known and used insofar as the coverage obtained thereby. In particular, typical zinc-rich coatings provide a film on the order of 1.5 to 2 mils thickness, whereas the coating material of the present invention may be applied so as to provide a 5.0 mil thickness, thereby assuring for complete and effective coverage.
Yet additional advantages of the corrosion resistant primer material of the present invention over comparable zinc-rich primer materials will be seen from the fact that zinc-rich coatings are extremely difficult to "clean up" and frequently require the use of mechanical abrasion means during a cleaning operation. The coating material of the present invention, on the other hand, may be cleaned up merely with the use of mineral spirit solvents or the like. Further, the primer material of the present invention has been found to be exempt from O.S.H.A. Rule 66, whereas certain types of zinc-rich primer materials are subjected to O.S.H.A. statutory limitations.
Another objectionable criticism to which zinc-rich primers have been subjected resides in the fact that the equipment used to apply the same must be cleaned with a suitable solvent material on a twice-daily basis in order to maintain such equipment operating satisfactorily, and that such equipment cannot be left unattended without cleaning for any period of time without subjecting such machinery to damage. The primer material of the present invention, on the other hand, can be left for limited periods of time without requiring cleaning and only periodic cleaning of the application equipment is all that is necessary.
Zinc-rich primers have also been found to be objectionable from the standpoint that they can only be used with spotwelding operations. The primer material of the present invention, on the other hand, may be used with spotwelding equipment, as well as with resistant welding apparatus. Further, zinc-rich primers, as they are being applied, must be constantly agitated thereby requiring special agitating equipment, whereas the primer material of the present invention needs no agitation under most circumstances, thereby obviating the need for such ancillary equipment.
Other advantages of the present invention over zinc-rich type primers of the prior art will become apparent from the following detailed description of the present invention, and it is a general object of this invention to provide a new and improved corrosion resistant primer which embodies all those features and advantages that have herebefore been stated and which will hereinafter become apparent.